Add aggressive coarsening + second step to RugeStuben for AMG + some other options

[moyner]

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[github-actions]

Remaining comments which cannot be posted as a review comment to avoid GitHub Rate Limit

Runic

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Jutul.jl/test/ka_preconditioners.jl

Line 646 in 63e1329

scaled = setup_amg(csr_matrix(scale*A; backend), options)

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Jutul.jl/test/ka_preconditioners.jl

Line 649 in 63e1329

resetup_amg!(H, csr_matrix(scale*A; backend), :sparsity)

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Jutul.jl/test/ka_preconditioners.jl

Line 659 in 63e1329

B = A + spdiagm(0 => [0.2 + 0.1*sin(i) for i in 1:size(A, 1)])

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Jutul.jl/test/ka_preconditioners.jl

Lines 661 to 664 in 63e1329

	interpolation = TwoStageExtendedIInterpolation(max_elements = 2,
	stage_max_elements = 2, rescale = rescale)
	options = AMGOptions(aggressive_levels = 1, aggressive_interpolation = interpolation,
	coarse_size = 1, max_levels = 2)

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Jutul.jl/test/ka_preconditioners.jl

Line 695 in 63e1329

end

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Jutul.jl/test/ka_preconditioners.jl

Lines 699 to 700 in 63e1329

	@test_throws ArgumentError setup_amg(poisson_2d(3),
	AMGOptions(interpolation = TwoStageExtendedIInterpolation()))

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Jutul.jl/test/ka_preconditioners.jl

Lines 722 to 723 in 63e1329

	@test all(i -> aggressive.levels[1].P.rowptr[i + 1] >
	aggressive.levels[1].P.rowptr[i], 1:size(A, 1))